全文获取类型
收费全文 | 373077篇 |
免费 | 29329篇 |
国内免费 | 355篇 |
专业分类
402761篇 |
出版年
2018年 | 8856篇 |
2017年 | 8598篇 |
2016年 | 8098篇 |
2015年 | 5361篇 |
2014年 | 6350篇 |
2013年 | 9051篇 |
2012年 | 11808篇 |
2011年 | 16668篇 |
2010年 | 12238篇 |
2009年 | 11326篇 |
2008年 | 14316篇 |
2007年 | 15933篇 |
2006年 | 9047篇 |
2005年 | 9292篇 |
2004年 | 8988篇 |
2003年 | 9015篇 |
2002年 | 8678篇 |
2001年 | 15588篇 |
2000年 | 15482篇 |
1999年 | 11751篇 |
1998年 | 3569篇 |
1997年 | 3681篇 |
1996年 | 3531篇 |
1995年 | 3226篇 |
1994年 | 3149篇 |
1993年 | 3070篇 |
1992年 | 9212篇 |
1991年 | 9000篇 |
1990年 | 9065篇 |
1989年 | 8657篇 |
1988年 | 8066篇 |
1987年 | 7654篇 |
1986年 | 6883篇 |
1985年 | 7193篇 |
1984年 | 5722篇 |
1983年 | 4984篇 |
1982年 | 3498篇 |
1981年 | 3258篇 |
1980年 | 3004篇 |
1979年 | 5380篇 |
1978年 | 4131篇 |
1977年 | 3776篇 |
1976年 | 3678篇 |
1975年 | 4284篇 |
1974年 | 4591篇 |
1973年 | 4716篇 |
1972年 | 4650篇 |
1971年 | 4253篇 |
1970年 | 3373篇 |
1969年 | 3149篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
992.
Some preliminary data regarding the test of penetration and proliferation of BHK and HeLa cells biocompatibility to a three dimensional stroma saturated with phosphorous and calcium salts (a biomaterial replacing bone) are presented. These data suggest that the analysed biomaterial might be used in surgical practices of prosthesis appliance on interfaces of fractured bone. 相似文献
993.
Interaction of netropsin and distamycin with deoxyribonucleic acid: electric dichroism study 总被引:13,自引:0,他引:13
We report dichroism and equilibrium binding studies of netropsin (Net) and distamycin A3 (Dist) binding to deoxyribonucleic acid (DNA). We show that at low degrees of binding (r) to calf thymus DNA, Net induces a considerable increase in the apparent DNA length (14 A/drug molecule bound), closely analogous to the results reported earlier for Dist. In addition, we show that chicken erythrocyte DNA shows length changes similar to those of calf thymus DNA upon distamycin binding. DNA length reaches a maximum at 1 bound drug/20-30 base pairs and then decreases to its initial value by r = 0.1. This effect is not seen for two other DNAs with nearly identical A + T base pair content and may therefore arise from the details of base sequence or base modification in eukaryotic DNA. We also show that Dist binding to calf thymus DNA at low r values is positively cooperative and shows a DNA affinity which is primarily nonionic. We demonstrate that independent of the DNA to which they are bound, the Net and Dist transition moments are inclined by 43 +/- 3 degrees from the helix axis, consistent with the idea that both drugs bind inside and parallel to the DNA small groove. From dichroism measurements, we show that the conformational change induced in calf thymus DNA by Dist does not kink or bend the helix and does not substantially alter the average inclination of the bases. Finally, we outline a statistical mechanical theory for calculation of binding isotherms when binding is coupled to a DNA structural change. 相似文献
994.
N. KINGSTON JAMIE K. MORTON ROBERT DIETERICH 《The Journal of eukaryotic microbiology》1982,29(4):588-591
Twenty-nine (64.4%) of 45 reindeer, Rangifer tarandus, examined over a two-year period were infected with trypanosomes. Trypomastigotes and dividing epimastigotes were found in the blood of fawns, cows, and bulls. Morphometric analysis of bloodstream trypomastigotes from reindeer and comparison of these parasites with similar stages of trypanosomes from elk, mule deer, and white-tailed deer from the contiguous United States proved them conspecific; the trypanosomes from these members of the Cervidae are identified as Trypanosoma cervi Kingston & Morton, 1975. This is the first report of trypanosomes from reindeer. No pathogenic effects are known to be caused by these parasites. 相似文献
995.
A simplified method of manual calculation for inbreeding coefficient (and/or relationship) from complicated pedigree tables presented in a nongraphic mode is offered. The method is based on the use of positional dual codes of ancestors in which all genealogical links of the proband are reflected. 相似文献
996.
N Durán Y Makita L H Innocentini 《Biochemical and biophysical research communications》1979,88(2):642-648
The presence of enzymically generated triplet acetone in red cells and energy transfer to eosin, rose bengal and 9,10-dibromoanthracene-2-sulfonate was indicate by: (1) product distribution; (2) KET τo, similar to the 2-methylpropanal/peroxidase/O2 system; (3) correlation between hemolysis, oxygen uptake and photon emission; (4) membrane protection by energy acceptors, and (5) by comparison of the 2-methylpropanal/peroxidase/O2 system with 2-methylpropanal/red cells/membranes/O2 and 2-methylpropanal/acid extractable protein from red cells membrane/O2 systems, which have a high peroxidase activity.This is the first report of a biological system producing a photohemolysis effect in the dark. 相似文献
997.
V. S. Kurbanismailov O. A. Omarov G. B. Ragimkhanov M. Kh. Gadzhiev M. G. Bairkhanova A. J. Kattaa 《Plasma Physics Reports》2011,37(13):1166-1172
The experimental results on the formation and development of initial stages of an impulse breakdown in atmospheric-pressure
argon at townsend and streamer breakdown mechanisms for different initial conditions are presented. A streamer channel is
shown to be initiated by bright luminescence formed at the point of critical avalanche amplification at different distances
from the cathode depending on overvoltage. Prebreakdown currents are experimentally measured for the townsend and streamer
breakdown mechanisms and peculiarities of spark channel formation for these mechanisms are studied. 相似文献
998.
Merkel cell tumor: diagnosis, prognosis, and management 总被引:2,自引:0,他引:2
The histologic features of the Merkel cell and the pathologic characteristics of the Merkel cell tumor are described. From a literature review, 68 cases are examined; 23 cases that have been followed up accurately are presented from the Mayo Clinic. A representative case is used to demonstrate the problems of diagnosis and suggested treatment. The latter should be wide local resection with removal of nodal metastases if present. When indicated, this should be followed up with radiation therapy. Chemotherapy is of little or no value. Survival rates are presented. 相似文献
999.
The role of duplication in the expression of a variable surface glycoprotein gene of Trypanosoma brucei 总被引:1,自引:0,他引:1
The variable surface glycoprotein (VSG) genes of Trypanosoma brucei have been classified into two groups depending upon whether or not duplication of the genes is observed when they are expressed. We report here the observation of duplication apparently linked to expression of the ILTaT 1.3 gene in the ETaR 1 trypanosome stock. In the ILTaR 1 stock, expression of the ILTaT 1.3 VSG did not involve a new duplication, but instead activation of a preexisting gene copy that had been apparently generated earlier by a duplication event analogous to that directly observed in the ETaR 1 trypanosomes. The results suggest that the well-characterised gene duplications found with other VSG genes are common to all VSG genes but are not directly responsible for controlling expression. All currently available data can be accommodated by a model that assumes that gene duplication and replacement occurs independently of antigenic switching. 相似文献
1000.
The paper analyzes humus profiles of mountain-chestnut soils of a complex catena situated within the Khemchik dry-steppe area
of the Central Tuva Depression. The study has shown that humus profile characteristics are determined by both slope aspects
and position in the catena. Humus profiles imprint all environmental changes of soil formation and functioning even if these
changes are not expressed in soil morphology. The materials obtained during the study may serve as basis for long-term monitoring
of slope soil behavior and for revealing local soil variability in changing environment. 相似文献